Process for purifying nitriles



PROCESS FOR PURIFYING NITRILES I Filed March 23, 1938 0 1o zo3o4o5oeo1oso9o1oo v PERCENT TOTAL DISTILLATE Wilbur AlLa z'gr,

George Rlgby INVENTORS BY v ' A TTORNEY 1 Patented May 1941 Wilbur .4;

& Company, W Delaware mm and George w. mm. Wilmington, Del., assignors to E.

I. du Pont de Nemonrs M, a corporation f App ication March 23, less, Serial No. 197,626

' Claims. 01. zoo-404) Y Thisinvention relates to the purification of nitriles', and more particularly to the purification of aliphatic dinitriles, and still more particularly'to the purification of adiponitrile.

The usual method of purifying nitriles is by vacuum distillation (seeOrganic Syntheses, Coll.

.vol. I,pp. 38, 101, 500 and 521). For most purposes the nitriles so obtained are sumciently pure to be used in subsequent chemical reactions.- "However, the products usually darken on standing and in some cases hydrogen cyanide is evolved. 1 The presence of hydrogen cyanide is well known to be very harmful to active hydrogenation catalysts such as finely divided nickel. In the presence of largeamounts of hydrogen cyanide the catalyst is rendered completely intacting the nitrile with sulfurous acid or with,"

a water-soluble salt thereof.

Thus, for example, crude I adiponitrile -is washed with an aqueous solution of ammonium bisulfite. The oil is then washed with water to remove dissolved bisulfite ions.

' purified may be hydrogenated directly to hexaactive while the presence of smaller amounts greatly diminishes the activity of the catalyst and thereby lowers the yield of primary amines which are obtained by the hydrogenation of the nitrile.

tar-like products which foul the hydrogenation catalyst and reduce the yield of the desired products. Finally these colored materials are not removed during the hydrogenation. They impart their color to the amines produced and render the latter unsuited for many uses until they have been carefully purified. This is both troublesome and expensive.

Aliphatic dinitriles, such as adiponitrile, are

particularly difilcult to obtain pure; i. e., with constant and reproducible physical properties.

- The accompanying drawing represents a graph comparing the properties of adiponitrile prepared by the catalytic dehydration of a mixture of adipic acid and ammonia vapors and purified by the usual distillation method, with the properties of the same adiponitrile purified by the invention described herein. Curve 1 records graphically the refractive indices obtained on successive fractions during a typical vacuumdistillation of adiponitrile. As a contrast, curve 11 records graphically thevrefractive indices for similar fractions of adiponitrile purified by the method of this invention.

The color which develops in nitriles seems to be associated with the formation of Per cent I Cyclopentanone. 2.5- Adiponitrile 80.4

'Ammonia 2.6 Residue 4a5v Total 99.0

The object of this invention, therefore. is to provide a simple, effective, and inexpensive method ofspurifying nitriles and particularly to provide such a method for purifying aliphatic dlnitriles. A further object of this invention is.-

to obtain aliphatic dinitriles of improved quality as measured by stability to light and air, and

' possessing constant and reproducible p y cal properties; A still further object of this inventicn-is to obtain adiponitrile as an essentially pure compound. Other objects will appear hereinaften, w j

These objects'are by P tion process which comprises the step of col}- Lazier, Serial No. 133,275, by passingmethylene diamine, as described in Examplelv. ,On the other hand, it maybe dried either by heating to drive off the water or by other suitable. means before use. If desired, the nitrile may be further purified by vacuum distillation. As obtained by the latter method, adiponitrile is a colorless, odorless, slightly viscous oil'hav- Nsrises mustacand B. P. 154 (1/10 mm.

' Example 1' Crude adiponitrile was prepared according to the copending U. 8. application of Wilbur A. the vapors of adipic acid. together with ammonia, over silica gel at 350 C. The product was vcondensed, and the aqueous layer drained off. The oily layer had the following analysis:

A. The crude nitrile was divided me two por-- 1 tions. One portion was distilled through an'efiicient fractionating column at 1! mm. of mercury pressure with the following results:

Percent Fraction number N total distillate 1 l. 4568 4. a 1. 4400 7. a 1.4895 11. 4 1.4403 13. 5 1. 4403 15. 6 1. 4306 16. 7 l. 4393 23. 8 1. 4385 34. a 1. 4381 42. i0 1. 4379 51. 11 1. 4378 100.

These results are recorded graphically in curve I.

The purified adiponitrile, upon standing 2!. hours in a partially filled bottle in the presence of light and air, turned darlrin color and gave of! the odor of hydrogen cyanide: also this product gave a-precipitate on addingfive drops of Adiponitrileso presence of adilute mineral acid at room temperature.

B. The second portion of the crude nitrile I was treated according to the process of the present invention:

Four hundred parts by weight of the crude adiponitrile having the composition indicated was mixed with 30 part of water and the solution treated with sulfur dioxide until the odor of the latter was plainly noticeable. The gas flow was then interrupted and the liquid was vigorously stirred at room temperature for six hours. The dark colored lower layer was separated and the remaining oil was washed with two 30-part portions of saturated ammonium bisulfite. The oil was then separated and washed twice with 30 part of water, then twice with 30 parts of 28% aqueous ammonia and finally twice with 30 parts of water. The product was distilled with the following results. using the same distillation apparatus and conditions as were used in Part A above. The results are recorded graphically in curve 2 and numerically below:

Percent Fraction number total distillate mNaOIIFHMi- The pure adiponitrile (fraction 6) was a colorless, mobile oil having a density Di 0.9596 It did not develop .color or hydrogen cyanide on standing 24 hours in a partially filled bottlereagent.

v ammonia, together wit urated sodium 2,242,909 17% hydrochloric acid to 5 cc. of said nitrile or hydrogen cyanide on standing 24 hours in the presence of sunlight and moisture in a partially filled bottle. Hydrogenation with a Raney nickel catalyst in the presence of ammonia yielded 90.7% or hexamethylene diamine. This 'example illustrates a modification in the. washing. of bisulflte treated crude nitrile satisfactory for semiplantuse. Example III Crude adiponitrile was prepared by passing the vapor of adipic acid, over a silica gel catalyst at 350 C. After separating the oily layer from the chilled prod- Three hundred and two parts of adiponitrile having the above analysis was evacuated until all of the ammonia had been driven oil, then 5 parts of concentrated hydrochloric acid was added and the mixture thoroughly agitated. As soon as the initial reaction had subsided. 100 parts of a saturated, solution of sodiurn bisulfite was added and the mixture thoroughly stirred during 12 hours. A semi-solid mass of crystals was thus obtained. After filtering off the crystals and washing them with benzene theoombined filtrates were washed twice with 30 parts of satbisulfite, then with 80 parts 0! H20 and finally with 30 parts of concentrated aqueous ammonia. The oily layer was then subjected to vacuum distillation. After removal of the benzene the nitrile was fractionallydistilled which was found of nitrile followed by the addition of Nesslers s Hydrogenation of the nitrile m the presence of 75 parts of ammonia per 100 part of nitrile. using 10 parts of an active nickel-on-alumina catalyst yielded 6.1% hexamethylene imine, 90.7% hexamethylene diamine, and 3.2% of residue. This example clearly demonstrates the advantage to be gained by purifying adiponitrile with abisulfite solution prior to distillation. Curves I and II graphically contrast the results of the two methods of purification.

Example H Two hundred and fifty parts of crude adiponitrile prepared as in Example I and having essentially the same analysis was treated with 24.3

parts of sulfur dioxide. The mixture was stirred during 8 hours; then the aqueous layer was separated and v the residual oil was washed four times with water using 17.5 parts of water for each washing. After careful fractional distillation the nitrile had a refractive index of N,1.4368 The water-white nitrile did not develop color at 10 mm. pressure with the following results:

' Percent Fraction number N total distillate v 1.4378 100.0 Residue 0.5%

g The material obtained as fraction 6 was a colorless oil which did not darken ordevelop hydrogen cyanide after standing in a partially filled bottle for 24 hours exposed to light and air. This oil did not give a precipitate when treated with a few drops of concentrated hydrochloric acid followed by an excess of Nesslers reagent. Hydrogenation with 10% of a catalyst composed of active'nickel supported on alumina in the presence of ammonia gave 90.7% of hexamethylene diamine, 5.9% of hexamethylene imine, and 3.4% of residue. This example illustrates the use of sodium bi'sulflrte and the acidification of the crude nitrile with hydrochloric acid prior to the bisulfite treatment. The conminimized by removing disused as a solvent for. the nitrile.

Example I V Adiponitrlle was prepared by passing the vapors of adipic acid together with ammonia over oily layer it was found to contain 19.1%

a silica gel catalyst at 350 C. The product was partially condensed by a proper control of the temperature at which the condensation took place. In this manner a (product having the following analysis was obtai ed:

Two hlmdred and twenty-four parts of ads ponitrile having the above analysis was treated with 6.1 parts 01' sulfur'dioxideand 11.0 parts of 73% ammonium bisulfite solution. The mixture was thoroughly agitated during 6 hours, 4 then the bisulfite solution was removed and the residual oil was washed three times with 10 parts of distilled water and once with 10 parts of 28% aqueous ammonia. Without fur- 2 ther purification, 100 parts of the above oil was hydrogenated with 75 parts of liquid ammonia and 10 parts of a Raney nickel catalyst. Hydrogenation proceeded at a normal rate (1% hours at 120 C. and 2000 pounds pressure) and the product contained 75.3 parts of hexamethylene diamine, 6.3 parts of hexamethyle'ne lmine and 8.0 parts of residue. This example illustrates the possibility of hydrogenating bisulfite treated adiponitrile directly without removing dissolved water and without distillation. It will be noted that the yield of diamine is fully as high as when the nitrile is distilled (allowance being made for the water present). The

quality of the diamine was fully as good as that obtained from distilled adiponitrlle.

Example V Crude adiponitrile was prepared by passing the vapors of adipic acid over silica gel at 350 C. in

the presence of ammonia. After separating the adiponitrlle.

One hundred and ninety-seven parts of this oil was treated with 2.8 parts of sulfur di-' oxide and was then washed four times with 20 parts of saturated sodium chloride solution and finally once with 20 parts of aqueous ammonia. The oil thus obtained was subjected to 1y diminishes the solubility: of adipqnltrile m 1 water and thus enhances the yield oi purep'roduct'obtained. The nitrile may-be usedas the crude oil .or may be a distilled product or may be dissolved in'a suitable inert solvent suchas The temperature at which the bisulfite treat! ment takes place may be varied within fairly wide limits. However, for convenience in operation it has been found desirable to work at. or

0 near room temperature. Thus, temperatures of from 0 to 100 C. are operable, although it is preferred to work in the range of from 20to C. since the losses of ammonia and sulfur dioxide are not serious at these temperatures.

The method known to the art, for purifying nitriles is to vacuum distill the cr'ude'materials, but the products thus prepared darken and liberate hydrogen cyanide withina short time when stored ina partially filled bottle in the presence of light and air. Within twenty-four hours the nitrile so prepared is also black; the exact nature of this darkening was not understood and was usually considered a characteristic property of the nitriles. "We have now found that pure.

7 nitriles are "perfectly stable under'thesc condltions. The present invention provides the only simple, practical, inexpensive, and eflec'tivemeans known to use by which these pure nitriles may be obtained. Nitriles purified in accordance with this invention have been stored as long as six months without darkening appreciably.

It is apparent that many widely diflerent embodiments of this invention may be made without departing from the spirit and scope thereof and therefore it is not intended to be limited excent as indicated in the appended claims.

We claim:

1. A process for the purification of an aliphatic dinitrile which comprises washing said aliphatic fractional distillation at 10 mm. pressure using 50 'dinitrile with a solution containing a bisulfltea 13 transier unit column. In this way 159 parts of pure adiponitrile was obtained. This is 96% of the theoretical amount present in the original oil. The refractive index of this oil at 25 C. was 1.4370. The material was waterwhite and had a density at 25 of 0.9596. It did notdevelop color or hydrogen cyanide on standing 24 hours in a partially filled bottle exposed to light and air.

amount. This example illustrates the use of brine solution in washing the nitrile to diminish losses due to the solubility of adiponitrlle in water.

adiponitrile, alpha, alpha'-dimethyladiponitrile, 7

octa-decyladiponitrile, and other similarly sub-' stituted aliphatic dinitriles maybe used in this process. It has been found preferable to use acidulated ammonium bisuliite although sodium Hydrogenation with a modified Raney nickel catalyst yielded 90% or hexa- 0 methylene diamine based on the theoretical 2. A process for the purification oi adiponitrile which comprises bringing said adlponitrile into contact with a solution containing a member selected from the group consisting of suli'urous acid and its water soluble salts.

3. A process for the purification of an aliphatic dlnitrile which comprises washing said aliphatic washing the resulting compound with water to remove the bisulfite, and then distilling the'prodact to recover the aliphatic dinitrilc.

5. The process for the purification of an all phatic dinitrile. prepared by the catalytic deny-- dration of the corresponding ammonia-acid derivative at elevated temperatures, which comv prises treating said dinitrile with a compound selected from the group consisting acid and its water-soluble salts.

6. 'lheprocessinaccordancewithclaim5 charofsulfurous bis'ulfitc, potassium bisulfite, or neutral or alkain that the dinitrile' is adiponitrile.

7. The process for the purification of adiponitrile, prepared by catalytically dehydrating an ammonia-adipic acid derivative at elevated temperatures, which comprises treating said adiponltrile with a bisulfite in an 'amount equivalent to about 3% to about 10% by weight of the nitrile.

8. The process in accordance with claim 7 characterized in that the bisulfite 1s ammoniuni bisulflte and that it is in active solution in admix-. ture with adiponitrile.

9. A process for the purification oi crude adiponitrile of composition similar to that obtained when adipic acid and ammonia, are dehydrated over silica. gel at about 350 C., which comprises treating said crude adiponitrile with a saturated aqueous solution of sulfur dioxide, separating the resulting adiponltrile and washing same with ammonium bisulflte, then removing the bisultlte and distilling the resulting product so as to. recover substantially pure adiponitrile.

10. A process for the purification of crude adiponitriie of composition similar to that obtained when adipic acid and ammonia are dehydrated over silica gel at about 350 0., which comprises treating said crude adiponitrile with a saturated aqueous solution of sulfur dioxide, separating the resulting adiponitrile and washing same to re- .move sulfur dioxide and compounds containing same.

WILBUR A. LAZIER.- GEORGE W. RIGBY.

Certificate of Correction Patent No. 2,242,309. May 20, 1941.

v WILBUR A. LAZIER ET AL. It is hereby certified that errors appear in the rinted specification of the above numbered patent requiring correction as follows: age 2, first column, line 42, for

D2 read Di; line 47, for 1.0% read 0.1%; page 3, second column, line 38, for the word use read us; and that the said Letters Patent should be read with these corrections therein that the samemey conform to the record of the case in the Patent Signed and sealed this 1st day of July, A. D. 1941.

HENRY VAN ARSDALE,

Acting Co nmiesioner of Patents. 

